The present invention relates to an illumination light source unit to be used for a liquid-crystal projector and the like and is designed for efficient reflection of light rays.
In the case of an illumination light source unit to be used for a liquid crystal projector, a light source lamp is placed at the focal point of a parabolic reflector so that the light rays emitted from the light source lamp are reflected by the parabolic reflector to be outputted as.parallel light rays. However, the light rays reflected near the optical axis (near the base of the light source lamp) are diffracted by being reflected by the surface of a spherical lamp due to the effect of the shadow of the light source lamp, so that the diffracted light rays cannot be used effectively as parallel light rays.
The present invention is intended to eliminate the problem of the prior art and designed to increase the luminance of the projected picture by converting into parallel rays the light rays reflected near the optical axis of the parabolic reflector of the illumination light source, thereby improving the utilization rate of the light source.
The present invention is intended to resolve the above-mentioned problem and the reflector of the illumination light source unit according to the present invention comprises a first parabolic reflector, for reflecting light rays coming from a light source lamp, having a paraboloid with a focal point coincident with the center of the light-emitting part of the light source and forming a portion of the reflector not including the portion corresponding to the external contour of the light source lamp with respect to the optical axis as being the center thereof, a second parabolic reflector forming the portion of the reflector, for reflecting light coming from the light source lamp towards the rim of the opening of the first parabolic reflector, not including the first parabolic reflector but including a paraboloid having a focal point eccentric from the center of the light-emitting part of the light source lamp, and a bottomless circular truncated conic reflector so that light rays from the light source are reflected to become parallel light rays to be outputted.
The first parabolic reflector, the second parabolic reflector and the circular truncated conic reflector may be formed integrally, or the circular truncated conic reflector alone may be formed separately to be mounted on the rim of the opening of the first parabolic reflector.
All the reflecting surfaces of the first parabolic reflector, the second parabolic reflector and the circular truncated conic reflector may be provided with a dichroic reflecting film capable of reflecting only the visible light rays respectively, or the reflecting surfaces of both the first parabolic reflector and the second parabolic reflector may be provided with a dichroic reflecting film capable of reflecting only visible light rays while the reflecting surface of the circular truncated conic reflector may be provided with a metallic reflecting film or may be made into a total reflector provided with an aluminum reflecting surface. When providing the circular truncated conic reflector as a total reflection reflector, it is preferable to be formed independently for ease of forming.
Further, the first parabolic reflector and the second parabolic reflector may be formed of glass, and the reflecting surfaces thereof may be provided with a dichroic reflecting film capable of reflecting only visible light rays.